Well logging, also known as borehole logging, is the practice of making a detailed record (a well log) of the geologic formations penetrated by a borehole. Resistivity logging is a method of well logging that works by characterizing the rock or sediment in a borehole by measuring its electrical resistivity. Resistivity is a fundamental material property which represents how strongly a material opposes the flow of electric current. Most rock materials are essentially insulators, while their enclosed fluids are conductors. Hydrocarbon fluids are an exception, because they are almost infinitely resistive. When a formation is porous and contains salty water, the overall resistivity will be low. When the formation contains hydrocarbons, or contains very low porosity, its resistivity will be high. High resistivity values may indicate a hydrocarbon bearing formation.
In one aspect, embodiments disclosed herein relate to a resistivity measuring tool used in a drillstring having a drill bit on a distal end for drilling a wellbore in a formation including a tool body having a longitudinal axis, a sensor configured to measure the angular position of the tool body relative to the wellbore, at least one axial antenna including a wire winding for generating an axial magnetic moment parallel with the longitudinal axis, and at least one transverse antenna. The transverse antenna includes an antenna body disposed within a pocket extending radially inward from an outer surface of the tool body and one or more turns of wire wound around the antenna body, the wire winding generating a transverse magnetic moment orthogonal to the longitudinal axis. At least one antenna is configured to transmit electromagnetic energy into the formation and induce a voltage signal related to a parameter of the formation in a different antenna.
In other aspects, embodiments disclosed herein relate to a method of making resistivity measurements of a formation from a wellbore being drilled including providing a resistivity measuring tool including a tool body having a sensor configured to measure the angular position of the tool body relative to the wellbore, at least one axial antenna including a wire winding for generating an axial magnetic moment, and at least one transverse antenna disposed proximate to an outer surface of the tool body and including a wire winding for generating a transverse magnetic moment. The method further includes transmitting electromagnetic energy into the formation from at least one of the antennas, thereby inducing a voltage signal related to a formation parameter in the wire winding of a non-transmitting antenna, measuring an angular position of the tool body relative to the wellbore with the sensor, and correlating the formation parameter with the measured angular position of the tool body.
In yet other aspects, embodiments disclosed herein relate to a method of making resistivity measurements of a formation from a wellbore being drilled including providing a resistivity measuring tool including a tool body having a sensor configured to measure the angular position of the tool body relative to the wellbore, at least two axial antennas each including a wire winding for generating an axial magnetic moment, and a transverse antenna disposed between the two axial antennas and including a wire winding for generating a transverse magnetic moment. The method further includes substantially simultaneously driving a current to the wire windings of the two axial antennas for generating a current loop in the formation, thereby inducing a voltage signal related to a formation parameter in the wire winding of the transverse antenna disposed therebetween, measuring an angular position of the tool body relative to the wellbore with the sensor, and correlating the formation parameter with the measured angular position of the tool body.
In still other aspects, embodiments disclosed herein relate to a method of data binning including partitioning a circumference of a tool face into M number of sectors, defining each data point relating to resistivity information by a fidelity function g(Φ), assigning to each data point a weight for each of the M number of sectors, wherein the weight is associated with an integral of the fidelity function g(Φ) over the sector, and computing an average of the data points weighted by their respective weights for each of the M sectors.